Significant advances have been made in the development of miniaturized electromechanical devices useful for a variety of purposes, such as electrical and optical switches. Examples of such devices are described in, for example, T. Earles, P. Mangat, J. Klein, and H. Guckel, "Magnetic Microactuators for Relay Applications," Proc. of Actuator 96, 5th International Conference on New Actuators, Jun. 26-28, 1996, Bremen, Germany, pp. 132-135, and U.S. Pat. No. 5,644,177, entitled Micromechanical Magnetically Actuated Devices. Such micromachined actuators are well suited for use in switches in which, generally, a stream of electronic, optical, or molecular flux is mechanically directed from a pole channel to either of two throw channels. Supplying a sufficient current to a drive coil switches the movable element of the actuator to one of its terminal positions; it can be returned to its other terminal position either by use of a second coil which is alternately activated or by a spring which biases the movable element of the actuator to its normal stationary or latched position when current to the coil of the actuator is cut off.
For many applications, it is desirable to be able to adjust the position of the movable element of an electromagnetic actuator, either continuously or in steps, until the element is at a position intermediate the terminal positions of the actuator. Examples of applications for such actuators include certain types of multi-position optical switches and computer hard drive head controllers. A micromechanical plunger supported by a spring, for example, may be drawn by the magnetic field from a drive coil, supplied with a selected level of current, to an intermediate position at which the spring return force is balanced by the magnetic attraction force from the drive coil. In order to provide sufficient positional accuracy for such a system, it is necessary to feed back a signal related to the displacement of the plunger to control the drive current to the coil so that the plunger reaches and remains at its desired commanded position. Some type of sensor must thus be used to detect the position of the plunger. Commonly used position sensors in larger mechanical systems include variable reactive elements, i.e., capacitors or inductors, the reactances of which change with the position of the moveable element. For example, a sensing coil may be mounted adjacent to a plunger formed of ferromagnetic metal such that the inductance of the sensing coil changes with the position of the plunger. However, in micromechanical systems, any sensing elements--coils or capacitors--must necessarily be quite small, so that the resistance of the element relative to its reactance is generally greater than would be found in sensing elements for larger mechanical systems. The relatively low Q factor for such micromechanical sensing systems thus makes the use of resonant circuit detectors of the type used in large mechanical systems subject to unacceptably large errors in sensing accuracy.